An ultrasonic-wave diagnosis apparatus is a non-invasive and highly safe medical diagnostic device for the human body and has a small apparatus scale compared with other medical image diagnosis apparatuses such as an X-ray diagnosis apparatus and a magnetic resonance imaging (MRI) apparatus. In addition, since the apparatus is capable of displaying in real time the state of motion of an examination target such as pulsation of the heart or movement of the fetus by simple operation of simply causing an ultrasonic-wave probe to abut from the body surface, the apparatus plays an important role in the medical care of today.
In the ultrasonic-wave diagnosis apparatus, ultrasonic waves are transmitted into a subject by supplying high-voltage drive signals to each of a plurality of oscillators incorporated in the ultrasonic-wave probe. The reflected waves of ultrasonic waves generated by differences in acoustic impedance of living tissues in the subject are received by each of a plurality of oscillator elements, and images are generated based on the reflected waves received by the ultrasonic-wave probe.
A transmission circuit which supplies high-voltage drive signals to each of the oscillators built in the ultrasonic-wave probe is composed of a high-withstand-voltage device so that high-voltage signals of Vpeak to peak of several tens to a hundred and several tens can be generated. Normally, a device with a structure that relaxes the electric field intensity between a drain and a gate such as laterally diffused MOS (LDMOS) is used for a high-withstand-voltage metal-oxide-semiconductor field effect transistor (MOSFET), and it requires an extremely large area to ensure a drift region between the drain and the gate. Therefore, when the transmission circuit is to be realized as an integrated circuit (IC: Integrated Circuit) on silicon, a large area is required.
On the other hand, since the reflected waves from the living tissues in the subject are affected by attenuation and diffusion in the living body, the amplitude of the reception signal subjected to acoustic-electric conversion by each oscillator is extremely small, and the reception circuit for subjecting this to amplification and signal processing is composed of a low-voltage device for the sake of low noise, low power consumption and small area.
Herein, each of the oscillators in the ultrasonic-wave probe is a transducer in which the same element carries out both of electric-acoustic and acoustic-electric, and both of the transmission circuit for supplying a high voltage to the same element and the reception circuit for receiving minute reception signals are connected. In this case, a switch is normally inserted between the oscillator and the reception circuit so that the reception circuit composed of the low-voltage device is not electrically destroyed when the transmission circuit supplies the high-voltage drive signal to the oscillator. This switch is referred to as a transmission/reception separation switch.
The transmission/reception separation switch becomes a switch-off state in a case of transmission to separate the reception circuit from the high-voltage drive signal generated by the transmission circuit and prevent electrical destruction. It becomes a switch-on state in a case of reception and has a role of causing minute reception signals from the oscillator to pass through with low loss. From the above roles, the transmission/reception separation switch is required to have electrical characteristics that can withstand high-voltage signals, and it is necessary to construct it with a high-withstand-voltage device.
In recent years, an ultrasonic-wave diagnosis apparatus capable of obtaining three-dimensional stereoscopic images has been developed, and examination efficiency can be improved by obtaining a tomographic image by specifying an arbitrary cross section from the three-dimensional stereoscopic image. For three-dimensional image-pickup, the oscillators in the ultrasonic-wave probe have to be changed from a conventional one-dimensional arrangement to a two-dimensional arrangement, and the number of the oscillators is increased to the second power compared with a conventional ultrasonic-wave probe. In this case, since it is practically impossible to increase the number of cables connecting the ultrasonic-wave probe and a main-device body to the second power, reception signals which have undergone reduction by phase-adjustment addition in the ultrasonic-wave probe have to be transferred to the main-body device via the cables. In order to realize the phase-adjustment addition in the ultrasonic-wave probe like this, the functions of transmission/reception and phase-adjustment addition are realized as a beamformer IC, transmission/reception circuits are disposed respectively for the oscillators in the IC to prepare pads electrically connected to the oscillators by one-to-one correspondence, and peripheral pads for transmitting outputs after the phase-adjustment addition to the main-body device are prepared separately from them.